To provide the house with the necessary amount of hot water an additional device is used - an indirect heating boiler (IHB). Its use can be considered one of the most rational and economically justified.
We will try to find out which scheme of indirect water heater piping is the most effective and how to connect the equipment to avoid common mistakes.
Content of the article:
- Choice of an indirect heating boiler
- Features of design and principle of operation
- Benefits of controlled equipment
- Types of devices with additional functions
- Size Tank size and importance
- Nuances of the piping devices
- Priority connection principle
- BCircuit diagrams and connection rules
- Possible #1 - piping with three way valve
- Possible #No.2 - scheme with two circulation pumps
- Variant #3 - piping with hydraulic arrow
- Variant #4 - use of recirculation
- Variant #5 - system with independent boiler
- How to connect the indirect water heater
- Conclusions and a useful video on the subject
Selection of the indirect water heater
Before buying and connecting the buffer tank accumulator (as the BNH is also called), you should understand the design features of the most popular types. The fact is that there are many types of equipment, including combined models that work from heating systems and alternative energy sources at the same time.
We will look at traditional coil boilers that use hot water as the heater.
The design features and principle of operation
What does indirect heating mean? Devices with direct heating function by means of a connection to electricity or a gas burner, BKNs have a different heat source. Water is heated by connecting to DHW, i.e. it turns out that the source is the heating medium - hot water (or its substitute).
The BKN resembles a standard water heater in appearance - that is it has a barrel shape, although modern models are more ergonomic. For ease of use and installation, they are given a rectangular configuration
If we consider new models of well-known brands, we can notice that gas boilers and CH boilers often have the same design. They are mounted side by side or one under the other - this way it is possible to save on the placement area.
The main element that performs the heating function is a steel or brass heat exchanger (coil) with a large surface area, which is located inside a metal, covered with a protective layer of enamel tank. In order not to cool the water too fast, the outside of the tank is surrounded with a layer of thermal insulation and some models are equipped with a casing.
If you want the water in the boiler to heat up quickly, choose a model with several exchangers and for the slow cooling down - with quality thermal insulation
A major detail, which now equips the most part of heating appliances, is a magnesium anode. The rod fixed in the upper part of the device protects the metal parts against corrosion, as a result the water heater serves much longer.
Barriers against high pressure action are the safety valve and the built-in thermostat. If the tank is not equipped with a safety group it is installed separately when fitting the piping.
Hot water heater's connection to the system
Powered water heater in combination with with the boiler
Application in the expansion tank bundle
Automation of the indirect boiler
Frequently the water circulating in the heating system does not exceed 65-70 °C. Many people doubt its efficiency when it acts as a heat source for heating in a BCH. In fact, the indicated temperature is sufficient, because the speed and magnitude of heat transfer depends largely on the area of (rather large) contact between the coil and the water.
How does the heating process work? The cold water intended to be heated enters through a separate opening and fills the entire vessel. From the boiler, water also enters the heat exchanger, but already heated. The hot coil walls transfer the heat to the cold water, which at the outlet already has a temperature suitable for showering or washing dishes.
Benefits of controlled equipment
The control capability is a characteristic that affects the assembly of the whole water heating system. There are two types of BCHs: simple (cheaper) and with a built-in control function.
The control of the heating process is mandatory if the main heating device - for example a gas or solid fuel boiler - has no control unit
A distinctive feature of controlled models is the additional equipment with temperature sensor and the possibility to supply/stop the water to the heat exchanger. Such equipment operates in automatic mode.
To start, it is necessary to connect:
- inlet/outlet for hot water from DHW;
- cold water supply to tank;
- collector for distribution of heated liquid at the outlet.
After that you can start the boiler - the water will start to heat up.
If the boiler is operating in automatic mode, the boiler control is not necessary. But it is better to equip it with a temperature sensor, there is a place for this in the casing
Wiring and piping of the indirect water heater is done by one of the ways (description below).
How can control affect the water temperature? Practically nothing. The maximum value that can be reached at the outlet temperature does not exceed the parameters of the coolant in the DHW system. Most likely it will be 1-2°C lower.
If more intensive heating is needed (this can happen if the boiler normally operates in low temperature mode), it is better to choose a model with built-in heating element.
It is advisable to buy such equipment together with solid fuel boilers (water remains hot even after the boiler has cooled down).
Variants of devices with additional functions
Tanks with a simple design are only part of the range presented in the water heating equipment market. There are many models of boilers whose functions are very useful for integration into a DHW system.
For example, one of the purposes of the more expensive models is to store heat. If there are possible power outages or the daily consumer rates are too high, an accumulation mode will be very useful. Design features of such models are reinforced thermal insulation and increased tank volume (300 liters and more).
Another option that realizes the fastest supply of hot water to the water drawing points is a recirculating boiler. Unlike the conventional design, this one has three connections to the hot water system. Two of them supply hot water, one - cold water. The water is supplied by means of a pump.
When using a model with recirculation, an additional useful circuit, e.g. for the installation of a towel warmer, can be arranged.
Rarer than units with coils, the \"tank-in-tank\" type models are found. The tank with the water to be heated is inside, the heating circuit outside
Water in such a tank is heated faster than in units with a heat exchanger, but the cost is also higher.
Tank size and its value
Cylindrical and cubic tanks differ in their dimensions. Their volume is indicated in liters: there are small models for 80-100 liters, but there are also bulky ones that hold up to 1400-1500 liters. The size is selected on the basis of the family's need for hot water.
Sizes are important for installation. Only light models are suitable for wall installation - up to 200 liters, all others have a floor version. Both the horizontal and vertical wall-mounted units come with special mountings, the floor-mounted ones are equipped with feet or a small stand.
The tubes required for water and coolant connection are usually drawn behind and above, to make connecting the tank to the pipes more convenient. The front panel of some models is equipped with a temperature sensor (relay) and a technical hole
Rectangular units take up slightly less space than cylindrical units due to their tight connection to the pipes.
Nuities of piping
It is easier to do the wiring and piping if the boiler is installed together with the boiler, pumps and other equipment involved in the DHW system assembly. Cutting an additional device into an existing network is much more difficult.
Either way, a number of rules will have to be followed in order for the appliances to work properly:
- choose the right installation place - as close as possible to the boiler;
- provide a flat surface for boiler installation;
- to protect against thermal expansion, install a membrane hydroaccumulator (at the outlet of heated water) with a volume not less than 1/10 of the BKN volume;
- fitting each circuit with a ball valve - for easy and safe maintenance of the units (e.g. three-way valve, pump or boiler itself);
- fitting of non-return valves in the water supply pipes to protect against backflow;
- improve water quality by mounting filters;
- fittingly position the pump (or several pumps) - the motor axis must be horizontal.
For safety reasons, no attempt should be made to fasten heavy devices to plasterboard or thin wooden partitions. Concrete and brick walls are suitable. Brackets or other types of holders are fastened with staples, anchors, dowels.
Depending on whether the unit is floor or wall-mounted, if possible mount it above the level where the boiler is installed or at the same level. For the floor standing appliance a pedestal or a stable support may be built up to a height of 1 m
When installing, the pipes are directed towards the boiler (even if disguised in the back or behind a false wall). Unreliable equipment such as corrugated hoses which cannot withstand the pressure and head of the water must not be used.
The following functional devices must be included in the piping for proper operation of the indirect storage water heater:
The complex technical system shall be equipped with pumps that supply hot sanitary water to the taps and encourage the flow of heating medium through the heating branch, and the water heating circuit in the boiler
Cold water from the common or autonomous water supply must be purified through a strainer or filter system that destroys lime salts before it enters the boiler. Filtration will prevent the formation of mineral sludge
After the strainer or water filtration system, a pressure reducer should be installed. But only if the branch pressure exceeds 6 bars
A check valve is needed before the cold water inlet in the boiler, to prevent backflow
To allow the heating water to have a reserve for expansion during periods when it is not being used, The piping must include an expansion tank and a safety valve to relieve pressure
To avoid unnecessary hot water in the taps, endangering burns, in the circuit must be installed three-way mixing valve. It will be mixed with hot water portions of the cold, as a result there will be water necessary for the user's temperature
To \"jacket\" heating sanitary water coolant from the heating came only when there is a need for it, set two-way thermostat. Its server is connected to the temperature sensor water heater
If the flow of hot water in the house is large enough, it is desirable to buy a boiler with an additional flow heater or buy a separate device and include it in the hot water supply branch. In case of shortage, a miniature flow heater will turn on and save the situation
Circulation and pressure pumps
Water pressure reducer
Feedback valve before boiler inlet
Safety valve safety valve and diaphragm chamber
Threeway mixing device
Two way heating circuit thermostat
Additional flow heat exchanger
Priority connection principle
Before installing the indirect water heater in the DHW system it is necessary to choose the connection principle: with or without priority. In the first case, when there is a need to get a large amount of hot water quickly, the whole volume of the heating medium is pumped through the BKH coil, which heats the water much faster.
After the water has reached the required temperature (measured by a thermostat), there is a way to redirect the flow to the radiators.
A non-priority connection does not allow the whole volume of heating medium to pass, and the boiler serves only a part of the total flow. With such a scheme the water takes longer to heat.
Boiler without priority connection: A separate circuit is connected to the boiler, therefore no possibility to cut off the radiators (or other heating devices)
The priority scheme is more efficient, as it allows a fast heating up of the required water quantity without affecting the heating. If the radiators are switched off for 30-50 minutes, the temperature in the rooms will hardly drop in this short period of time, but there will be enough hot water.
The only condition for the installation of the priority scheme is a powerful boiler.
Schemes and connection rules for BKN
The connection scheme and installation details for the indirect heating water heater depend on the class of the device and the heating system in the house. It is necessary to choose the right place of installation, focusing on the location of the boiler, cut-in pumps and existing wiring. Let's try to find out what should be taken into account when installing the heating equipment.
Application #1 - piping with three-way valve
This is one of the most popular schemes, as its application is a parallel connection of the heating system and the BKN equipped with a shut-off valve. The boiler must be installed near the boiler, the circulation pump must be installed in the flow, then the three-way valve.
This scheme is successfully applied when several heating appliances are used, e.g. two different boilers.
The three-way valve is a kind of switch which is controlled by a thermal relay. When the temperature drops, the automation triggers and the flow of the heating medium from the heating circuit is redirected to the BKH
It is essentially a priority system which ensures that the water in the boiler is heated quickly when the radiators are completely off for some time. As soon as the temperature rises to the set point, the three-way valve is actuated again and returns the coolant back into the heating system. This way of piping is useful for those, who use the boiler in the permanent mode
Application #2 - scheme with two circulation pumps
If a boiler is used rarely (for example, seasonally or at weekends) or if the water temperature is lower than in the heating system, the scheme with two water heating system with forced circulation: schemes, realization variants, technical details by circulation pumps is used. The first one is placed on the supply pipe, immediately before the BKN, the second one on the heating circuit.
The circulation pump is powered via a thermostat, therefore it only starts working when the temperature drops below the required one. The heating is accelerated when the forced circulation is started
This connection is not used in this scheme, the piping is equipped using simple connecting T-pieces.
Application #3 - piping with hydraulic arrow
This connection is used for large volume boilers (200 litres or more) and branched heating systems with many additional circuits. An example is the heating system in a two-storey house where floor heating is used in addition to a multi-circuit radiator system.
The hydraulic manifold is necessary to simplify the heating system layout and avoid installation of recirculation pumps for each heating circuit
The installation of a hydraulic manifold avoids heat shock as the water pressure in each circuit will be identical. It is rather difficult to make the piping yourself according to this scheme, so it is better to turn to professional installers.
Option #4 - use of recirculation
Recirculation is useful when there is a circuit that needs a constant supply of hot water - for example a towel dryer. If it is connected to the heating system, the coolant will circulate constantly and the dryer will function and serve as a heating device at the same time.
The use of recirculation has one big advantage - it is not necessary to wait for the water to heat to the right temperature, it will always be hot
But this scheme has disadvantages too. The main one is the increase in fuel costs, because it requires constant heating of the water cooled in the circuit. The second disadvantage is the mixing of water in the boiler. Usually the hot water is in the upper part, and from there goes to the drawing points, here it mixes with the cold, so the output temperature is slightly lower.
There are models of boilers with built-in recirculation, that is ready to connect the towel radiator. But it is cheaper to purchase a conventional tank, applying tees for connection.
Option #5 - system with energy independent boiler
The distinctive feature of this scheme is the installation of the boiler on a higher level than the boiler and heaters. Preference is given to wall mounted models which can be suspended 1 m above the floor.
Floor mounted models specifically in this scheme are inferior to wall mounted models in terms of heating speed and quality. The water temperature is much lower (approximately the same as in the return pipe), consequently the hot water reserve is lower
The energy independent type of heating is based on the application of the laws of gravity, consequently the heating medium will circulate even in case of power failure. Circulation pumps can normally be connected.
How to connect the indirect water heater
After selecting the circuit, it becomes clear what equipment is required. In addition to the basic devices, valves, ball valves, distribution valves, valves (three-way or return) may be needed.
Principle of operation:
- prepare installation site (floor or wall);
- make wiring by marking hot/cold water outlets in red/blue;
- install tee and pressure relief valve, securing connections with sealant;
- screw on the hot (top) and cold (bottom) water taps;
- connect to the power supply, install the thermostat and automatics;
- choose the heating mode;
- test the connection.
These are general recommendations necessary to present the scope of work. When connecting a specific model, follow the instructions provided with the model.
Conclusions and useful videos on the subject
How to determine the wiring diagram and correctly install the equipment will be explained in the following videos.
General information on connection diagrams:
Practical hints for the connection of the appliance:
How to correctly wrap an indirect heating boiler can be found in the following video:
Professional overview of an 80 l boiler:
Besides the installation and connection, regular maintenance is required. It consists of flushing the inner cavity of the tank, removing deposits and scale, replacing the magnesium anode. Maintenance of the equipment does not require much effort. If the strapping is done correctly, immediate repair is not required, but if you have problems with the equipment, we recommend contacting specialists.
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